Electrical Transport Properties Research Articles

Polarization-dependent electrical transport and thermoelectric properties in (010) surface of λ-Ti3O5

In recent research, the (010) surface of λ-Ti3O5 has demonstrated outstanding capabilities in light absorption and molecular adsorption, promising various applications. In this study, we employed density functional theory (DFT) to analyze the optical and thermoelectric properties of the (010) surface of λ-Ti3O5. Our findings reveal the excellent in-plane anisotropy of the optical anisotropy of bulk λ-Ti3O5 and thermoelectric properties in its (010) surface. The figure of merit (ZT) along the groove structure direction reaches 2.4, while the ZT perpendicular to it is only 0.85. In addition, the electrical transport characteristics along the (010) surface exhibit significant nonlinear characteristics. Our research results indicate that it has the potential to become a favorable material for optical and electronic devices.

One stone three birds: Natural mineral enhancing thermoelectric properties in Cu2Se-based composites

Copper selenide can be used in thermoelectric applications since it has the features of a superionic conductor. Nevertheless, improving its electrical and thermal transport properties using facile fabrication is challenging. Herein, a one-stone and three-bird strategy was proposed for enhancing the thermoelectric performance of Cu2Se-based composites. Natural verdigris was used as an additive to construct a porous structure simultaneously while introducing Cu vacancies and multiscale Cu2O precipitates in the Cu2-xSe material. The carrier concentration was tailored to optimize the electrical transport properties of the bulk composites. Additionally, multiple lattice defects were generated in the bulk composites, benefiting the significantly reduced thermal conductivity. Ultimately, the Cu2Se-based composite achieved a peak ZT value of 1.25 at 873 K. This study provided a simple approach of adding a natural mineral to regulate the composition and microstructure of the material, which may be worth promoting in other systems.

Modulation on the magnetic and electrical transport properties of Pr0.5Ba0.5MnO3-δ thin films by oxygen vacancies

In this work, the magnetic and electronic transport properties of the epitaxial Pr0.5Ba0.5MnO3-δ (PBMO) thin films via the modulation of the oxygen vacancies have been investigated. PBMO thin films were fabricated by pulsed laser deposition (PLD) at different oxygen ambient pressures (20, 50, 70, and 250 mTorr). From the XRD and STEM measurements, the oxygen vacancies content in the film increases with the decrease of growth pressure, leading to an expansion of the out-of-plane lattice constant of the film. The PNR (Polarized Neutron Reflectometry) was employed for a precise magnetization and oxygen stoichiometry depth profile of the PBMO thin films and further quantitatively characterize the oxygen vacancies’ content of the films. Thus, an increasing number of oxygen vacancies suppress the double exchange interaction and carriers hopping are suppressed, resulting in a significant increase in resistivity, as well as a decrease in saturation magnetization and ferromagnetic Curie temperature.

The electrical transport property and gas detection behaviour of polyvinyl alcohol and γ-Fe2O3 nanocomposite film

This paper presents the electrical and gas detection behaviour of polyvinyl alcohol (PVA)/γ-Fe2O3 nanocomposite films. The physical characterization includes X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and UV–Visible spectroscopy. The analysis of both the dc resistivity and ac conductivity using Correlated Barrier Hoping (CBH) conduction process shows that the conductivity enhances with the decreasing of activation energy in case of the PVA/γ-Fe2O3 nanocomposite film which is the indication of interfacial defect states. The current voltage study at various temperatures follows the thermoionic emission model of Schottky Barrier diode. Moreover, the dielectric constant enhances for PVA/γ-Fe2O3 nanocomposite film, which indicates homogeneous distribution of γ-Fe2O3 nanoparticles within PVA matrix and the aggregation of trapped charges found in interface develops an interfacial polarization. As a result, the gas adsorption capacity of the nanocomposite film increases which improves the signal-to-noise ratio, leading to higher gas detection sensitivity.

Crystallization behavior and structural characteristics of Cr-doped Sb70Se30 thin films for phase change memory

In this study, we prepare Cr-doped Sb70Se30 (SS) thin films via the magnetron sputtering. The influence of Cr doping on the crystallization behavior and structure characteristics of the SS thin films is systematically studied using a combination of experimental analyzes and theoretical calculations. The results reveal that compared with SS thin films, Cr-doped SS thin films exhibit higher crystallization temperature, better data retention capability, larger crystallization activation energy, and reduced resistance drift coefficient. In addition, the incorporation of Cr effectively suppresses grain growth in the SS thin films and refines the grain size. The electrical transport properties of the Cr-doped SS thin films are analyzed using a Hall system. Both X-ray photoelectron spectroscopy and first-principles calculations indicate that Cr is more prone to occupy Sb atoms and form stronger Cr–Se bonds, consequently enhancing the stability of the SS thin films. Raman spectroscopy confirms that the introduction of Cr leads to a decrease in bond length and an increase in bond energy. Moreover, the Cr-doped SS thin film exhibits minimal volume fluctuations and a smoother surface morphology, resulting in enhanced interface performance and reliability. Taken together, these results indicate that the introduction of Cr is an effective strategy for optimizing the properties and modifying the structures of SS phase-change materials.

Synthesis, characterization, and electronic transport properties of o-carborane-bridged thiophene derivatives

Here, α- or β-thiophene-substituted derivatives bridged by an o-carborane group were synthesized. Scanning tunneling microscope break junction techniques have revealed that the thiophene anchoring groups form a single-molecule junction with an Au electrode. Flicker noise analysis suggests the existence of through-space transmission pathways between the thiophene units. Furthermore, the electronic coupling of the β-thiophene substituted molecule with the electrode is found to be more stable, resulting in a 70 % increase in conductance compared to the α-isomer counterpart.These findings offer valuable insights for the design and development of o-carborane-based molecules, underscoring the significance of molecular backbones and substitution patterns on their electrical transport properties.

Assessment of Artificial Anisotropic Materials for Transverse Thermoelectric Generators

By alternately stacking layers of two materials that differ in their Seebeck coefficient and electrical and thermal conductivity, a composite material with artificial anisotropy of thermal and electrical transport properties is formed. Due to the transverse Seebeck effect, a thermoelectric (TE) voltage is generated perpendicular to a temperature gradient ΔT, that is applied at a certain angle φ with respect to the stacked layers (0° < φ < 90°). The TE properties of layered artificial anisotropic materials are described analytically using existing concepts and extending the available definitions to develop a consistent image of anisotropic media for TE energy generation. Based on these analytical descriptions, the TE performance of ceramic oxide–metal composites and transverse TE generators (TTEG) made of them are numerically calculated and presented in contour plots. These so‐called micro‐ and macro‐Babin plots map the influence of internal geometric parameters, i.e., the layer thickness ratio and the angle φ of the applied temperature gradient with respect to the stacked layers. Based on these diagrams, the optimal TTEG geometry can be narrowed down in a simple and fast way. In addition, the diagrams are used for a material screening to evaluate the suitability of different oxide ceramics for use in a TTEG.

Improving electrical transport properties of LaxCa0.89-xSr0.11MnO3 films via optimized La content

Optimized LaxCa0.89-xSr0.11MnO3 (x = 0.65, 0.68, 0.71 and 0.74) films were fabricated using spin-coating method. According to double exchange (DE) mechanism and Jahn-Teller effect, the enhancement of peak temperature coefficient of resistivity (TCR) was attributed to low residual resistivity and weak various electron scatterings, including electron–electron, electron–phonon and electron-magnon. Also, peak TCR temperature is not only influenced mainly by the DE mechanism, but also by the Mott transition. Moreover, optimized sintering improved film crystallinity, increasing peak TCR value. The resulting La0.71Ca0.18Sr0.11MnO3 film displayed a peak TCR of 10.74 %/K at 294.11 K. Appropriate chemical composition and sintering promoted the enhancement of electrical transport properties.

The effect of transition metal ion implantation on the structural and optical properties of few-layered borophene

Borophene, a monometallic two-dimensional layered material has gained significant attention due to its exceptional electrical and optical properties. Despite this, borophene layers tend to restack; retards ionic conductivity, imperative for practical applications. Thus, by introducing large-sized dopants into borophene nanosheets using an ion implantation technique has been acknowledged. Accordingly, herein, structural and electronic engineering of borophene has been done with implantation of copper (Cu) ions at various fluence rates (5 × 1012, 5 × 1013, 5 × 1014 and 5 × 1015 ions-cm−2 respectively) using 1μA current at a low energy of 80 keV. The Cu insertion between borophene interlayers prevents self-restacking; providing surfacial active sites with tunable work function and decreased band gap of pristine borophene, thereby increasing charge transport ability. Further, the structural properties of implanted borophene were characterized through Raman spectroscopy, FT-IR spectroscopy and optical properties using UV–Vis and photoluminescence studies. Also, I-V measurements were conducted to study the electrical properties. Hence, ion implantation helps in significantly enhance the electrical conductivity and transportation properties of borophene.

Ultralow thermal conductivity and high thermoelectric performance induced by dimensionality reduction in chain-like compounds X2PtSe2 (X=K, rb)

Balancing low lattice thermal conductivity (κL) with a high power factor is a major challenge in the research of thermoelectric (TE) materials. In this paper, we report on a class of chain-like compounds, X2PtSe2(X = K, Rb), characterized by strong lattice anharmonicity, weak bonds, and low phonon group velocities. Using first-principles calculations in conjunction with self-consistent phonon theory and the Boltzmann transport equation, we systematically investigate the thermal and electrical transport properties of X2PtSe2(X = K, Rb). At room temperature, the κL of K2PtSe2 and Rb2PtSe2 in the direction perpendicular to the Pt–Se chains is only 0.15 and 0.10 Wm−1K−1, respectively. Additionally, due to the low-dimensional nature of the Pt–Se chains, these compounds exhibit a ‘pudding-mold type’ band structure, contributing to a TE power factor. At 300K, under n-type doping, K2PtSe2 and Rb2PtSe2 achieve TE figures of merit (ZT) values of 1.66 and 1.67, respectively, in the direction perpendicular to the Pt–Se chains. At 500K, the ZT value of Rb2PtSe2 approaches 4, far surpassing traditional TE materials. These results indicate that the chain-like compounds X2PtSe2(X = K, Rb) exhibit excellent TE performance, achieving energy conversion efficiencies comparable to commercial transducer devices.

Optimized TCR and MR of La0.67Ca0.33-xSrxMnO3: Ag0.15 ceramics by Sr doping

Herein, in order to successfully create high-density La0.67Ca0.33-xSrxMnO3: Ag0.15 (LCSMO: Ag) ceramics (0 ≤ x ≤ 0.05), this research combines sol-gel and solid-phase processes. LCSMO: Ag ceramics electrical transport and magnetic properties were thoroughly investigated. XRD verified that the high-purity orthorhombic perovskite structure (space group Pnma) was produced. As Sr doping rises, the grain size grows, the single electron bandwidth increases, the metal-insulator transition temperature (TMI) continues to climb, and temperature coefficient of resistance (TCR) and magnetoresistance (MR) steadily drop. When x = 0.04, the TMI reaches 302.2 K. At this time, the TCR peak (TCRpeak) reaches 24.0 %·K−1 and the MRpeak reaches 49.2 %. These results demonstrate that Sr may effectively raise the TMI of LCMO: Ag ceramics to room temperature while maintaining high TCR and MR Values, which benefits the material's potential applications in devices such as uncooled infrared detectors.

Photocatalytic degradation of Rhodamine B dye via Bi2O3 embedded BaO-P2O5-TeO2 glass nanocomposites: An ab initio study of structural, optical, and electrical transport properties

Bismuth incorporated glassy systems with composition xBi2O3-(1-x) [0.3BaO-0.3P2O5-0.4TeO2] (where x = 0.10, 0.15, 0.20, and 0.25) are synthesized by melt quenching technique. The glassy systems are examined for their structural, and surface morphological properties using XRD, SEM, and EDX analysis. A study of photocatalytic activity for the degradation of common organic dyes like Rhodamine B (RhB) dye under visible light is also carried out. From UV-vis absorbance data, the calculated optical band gap energy values declined from (2.99-2.56) eV, whereas the Urbach energy and refractive index values increased from (0.35 -0.52) eV, and (2.39 - 2.52), respectively with the rise of Bi2O3 content(x). Additionally, the fundamental processes of electrical conductivity have been studied within the framework of Jonscher's universal power law and the Almond-West formalism. The Mott and Greaves model asserts that the small polaron hopping model underlies DC conductivity; as Bi2O3 content increases, DC conductivity rises, but hopping distance (Rhop) and hopping energy (Whop) drop dramatically. The electrical conductivity study reveals the semi-conducting nature of the as-prepared samples. In our present study, we are focusing on the structural, optical, and electrical transportation properties, additionally, we investigated this class of glassy materials as a promising candidate for photocatalytic dye degradation. Our study reveals that RhB dye can degrade up to 75% within 340 min of visible light illumination. Moreover, the test demonstrates the production of superoxide radicals by the CB-electrons and hydroxyl radicals by the VB holes enables efficient photocatalytic dye degradation.

Electronic, thermoelectric and electrical transport properties of single layer γ-graphyne

Recently, graphyne has emerged as the sole two-dimensional carbon material exhibiting both sp and sp2 hybridization. It’s remarkable attributes have ignited considerable interest, particularly in the realm of optoelectronics, driven by its narrow band gap, signifying its vast potential in this field. In this paper we investigated electronic, thermoelectric and electrical transport properties of single layer γ-graphyne systematically and comparatively by using density functional theory (DFT). Our findings reveal that γ-graphyne displays pronounced absorption peaks within both the infrared (IR) and visible regions (VR), indicating its robust optical characteristics. Additionally, γ-graphyne showcases exceptional thermoelectric performance. The insights gained from this study elucidate the properties of γ-graphyne and suggest its applicability across various domains, including optical sensing and thermoelectric energy conversion devices.

Effect of temperature on polaronic transport in CeO2 thin-film.

The outstanding catalytic property of cerium oxide (CeO2) strongly depends on the polaron formation due to the oxygen vacancy (V̈O) defect and Ce4+ to Ce3+ transformation. Temperature plays an important role in the case of polaron generation in CeO2 and highly influences its electrical transport properties. Therefore, a much needed attention is required for detailed understanding of the effect of temperature on polaron formation and oxygen vacancy migration to get an idea about the improvement in the redox property of ceria. In this work, we have probed the generation of polarons in CeO2 thin-film deposited on a silicon (Si) substrate using the resonance photoemission spectroscopy (RPES) study. The RPES data show an increase in polaron density at the substrate-film interface of the thermally annealed film, indicating the formation of an interfacial Ce2O3 layer, which is, indeed, a phase change from the cubic to hexagonal structure. This leads to a modified electronic band structure, which has an impact on the capacitance-voltage (C-V) characteristics. This result nicely correlates the microscopic property of polarons and the macroscopic transport property of ceria.

Momentum-Resolved Electronic Structures and Strong Electronic Correlations in Graphene-like Nitride Superconductors.

Although transition-metal nitrides have been widely applied for several decades, experimental investigations of their high-resolution electronic band structures are rare due to the lack of high-quality single-crystalline samples. Here, we report on the first momentum-resolved electronic band structures of titanium nitride (TiN) films, which are remarkable nitride superconductors. The measurements of the crystal structures and electrical transport properties confirmed the high quality of these films. More importantly, from a combination of high-resolution angle-resolved photoelectron spectroscopy and first-principles calculations, the extracted Coulomb interaction strength of TiN films can be as large as 8.5 eV, whereas resonant photoemission spectroscopy yields a value of 6.26 eV. These large values of Coulomb interaction strength indicate that superconducting TiN is a strongly correlated system. Our results uncover the unexpected electronic correlations in transition-metal nitrides, potentially providing a perspective not only to understand their emergent quantum states but also to develop their applications in quantum devices.

Crossover from Cooper-pair hopping to single-electron hopping in Pb x (TiO2) 1−x granular films

The electrical transport properties of Pb x (TiO2) 1−x (x being the Pb volume fraction and ranging from ∼0.45 to ∼0.72) granular films are investigated experimentally. The charging energy of the Pb granules is reduced to less than the superconducting gap of Pb granules for the low temperature insulating films by using high-k dielectric TiO2 as the insulating matrix. For the insulating films in the vicinity of the superconductor-insulator transition, Cooper-pair hopping governs the low-temperature hopping transport. For these films, the low-temperature magnetoresistance is positive at low field and the resistivity vs temperature for Cooper-pair hopping obeys an Efros–Shklovsii-type variable-range-hopping law. A crossover from Cooper-pair-dominated hopping to single-electron-dominated hopping is observed with decreasing x. The emergence of single-electron-dominated hopping in the more insulating films is due to the causation that the intergrain Josephson coupling becomes too weak for Cooper pairs to hop between adjacent Pb granules.

Piperidine and Pyridine Series Lead-Free Dion-Jacobson Phase Tin Perovskite Single Crystals and Their Applications for Field-Effect Transistors.

Two-dimensional (2D) organic-inorganic metal halide perovskites have gained immense attention as alternatives to three-dimensional (3D) perovskites in recent years. The hydrophobic spacers in the layered structure of 2D perovskites make them more moisture-resistant than 3D perovskites. Moreover, they exhibit unique anisotropic electrical transport properties due to a structural confinement effect. In this study, four lead-free Dion-Jacobson (DJ) Sn-based phase perovskite single crystals, 3AMPSnI4, 4AMPSnI4, 3AMPYSnI4, and 4AMPYSnI4 [AMP = (aminomethyl)-piperidinium, AMPY = (aminomethyl)pyridinium] are reported. Results reveal structural differences between them impacting the resulting optical properties. Namely, higher octahedron distortion results in a higher absorption edge. Density functional theory (DFT) is also performed to determine the trends in energy band diagrams, exciton binding energies, and formation energies due to structural differences among the four single crystals. Finally, a field-effect transistor (FET) based on 4AMPSnI4 is demonstrated with a respectable hole mobility of 0.57 cm2 V-1 s-1 requiring a low threshold voltage of only -2.5 V at a drain voltage of -40 V. To the best of our knowledge, this is the third DJ-phase perovskite FET reported to date.

Anionic Effect on Electrical Transport Properties of Solid Co2+/3+ Redox Mediators.

In a solid-state dye-sensitized solar cell, a fast-ion conducting (σ25°C > 10-4 S cm-1) solid redox mediator (SRM; electrolyte) helps in fast dye regeneration and back-electron transfer inhibition. In this work, we synthesized solid Co2+/3+ redox mediators using a [(1 - x)succinonitrile: x poly(ethylene oxide)] matrix, LiX, Co(tris-2,2'-bipyridine)3(bis(trifluoromethyl) sulfonylimide)2, and Co(tris-2,2'-bipyridine)3(bis(trifluoromethyl) sulfonylimide)3 via the solution-cast method, and the results were compared with those of their acetonitrile-based liquid counterparts. The notation x is a weight fraction (=0, 0.5, and 1), and X represents an anion. The anion was either bis(trifluoromethyl) sulfonylimide [TFSI-; ionic size, 0.79 nm] or trifluoromethanesulfonate [Triflate-; ionic size, 0.44 nm]. The delocalized electrons and a low value of lattice energy for the anions made the lithium salts highly dissociable in the matrix. The electrolytes exhibited σ25°C ≈ 2.1 × 10-3 (1.5 × 10-3), 7.2 × 10-4 (3.1 × 10-4), and 9.7 × 10-7 (6.3 × 10-7) S cm-1 for x = 0, 0.5, and 1, respectively, with X = TFSI- (Triflate-) ions. The log σ-T-1 plot portrayed a linear curve for x = 0 and 1, and a downward curve for x = 0.5. The electrical transport study showed σ(TFSI-) > σ(Triflate-), with lower activation energy for TFSI- ions. The anionic effect increased from x = 0 to 1. This effect was explained using conventional techniques, such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-visible spectroscopy (UV-vis), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA).

Crystal structure, magnetic and electrical transport properties of titanium-doped half-Heusler alloys Ni1−xTixMnSb

Ni[Formula: see text]TixMnSb polycrystalline alloys in the range [Formula: see text] were synthesized employing the standard solid-phase synthesis method. The crystal, magnetic, as well as electrical properties of the alloys were investigated using neutron powder diffraction and magneto-resistance measurements. The results reveal that the substitution of Ti for Ni within the temperature range of 2.5–300 K does not induce alterations in the crystal and magnetic structures of NiMnSb. The ordered Ni magnetic moment approaches zero. The study of the electrical transport properties of the Ni[Formula: see text]TixMnSb alloys, where [Formula: see text], has demonstrated a half-metallic state at low temperatures and metallic conductivity for temperatures exceeding 160 K. A semiconductor state manifests at titanium concentrations of x = 0.2 and was observed at temperatures below 21 K. The obtained experimental results are elucidated through first-principles theoretical calculations.

Advancing Thermoelectric Performance of Bi2Te3 below 400 K.

Thermoelectric cooling devices utilizing Bi2Te3-based alloys have seen increased utilization in recent years. However, their thermoelectric performance remains inadequate within the operational temperature range (≤400 K), with limited research addressing this issue. In this study, we successfully modulated the carrier concentration of the sample through Te content reduction, consequently lowering the peak temperature of the zT value from 400 to 300 K. This led to a substantial enhancement in thermoelectric performance at room temperature (≤400 K). Furthermore, by doping with La, the electrical transport properties have been further optimized, and the lattice thermal conductivity has been effectively reduced at the same time; the average zT value was ultimately elevated from 0.69 to 0.9 within the temperature range of 300-400 K. These findings hold significant promise for enhancing the efficacy of existing thermoelectric cooling devices based on Bi2Te3-based alloys.